The 2 biggest life altering changes i've seen in my pc were going to 8 gigs of ram from 4 and getting an SSD. I also play on a Q9550 and my cpu definitely pegs in TB and in Org central (i stick to the valley of honor to keep away from that). My graphics card is a geforce 260 and never gets to full use. I have all my settings on slaves turned down and I do get bad frame rates in huge fights or highly populated areas.

I'm planning on oc'ing mine to see if it helps, it just runs really hot and i haven't put the aftermarket cooler on the chip yet.